Conventional spotlight-mode Synthetic Aperture Radar (SAR) collects a set of data that represents the response (radar echo) produced by a target scene when illuminated by a sequence of radar pulses contained in a synthetic aperture. The collected data is processed into a SAR image. Customarily, a single coherent data set (single synthetic aperture) is used to form a single image. A sequence of SAR images is normally produced from a sequence of respectively corresponding synthetic apertures. Because each SAR image in the SAR image sequence is associated with a respectively corresponding synthetic aperture, the image rate of the sequence is limited by the time that is required to fly the length of the synthetic aperture. The flying time, and thus the image rate, is a function of range, and can be tens of seconds at long ranges. Such limitations on the image rate can impede the SAR system's ability to support detection of dynamic changes that are occurring in the target scene.
A faster image rate (also referred to herein as frame rate) would require either a higher platform velocity, or a shorter synthetic aperture. The velocity is limited by the aircraft or spacecraft capabilities. A shorter synthetic aperture typically requires either a range that is unacceptably short, or an image resolution that is unacceptably coarse.
It is desirable in view of the foregoing to provide for SAR image rates that permit detection of target scene dynamics.